KR100205492B1 - The control system of video signal processing apparatus - Google Patents

Abstract

A level setting means for adjusting the brightness (30) of a television receiver is modified by the setting of an amplitude control means for adjusting the contrast (20) such that the maximum brightness level of the image on a CRT is modified in direct relationship to the adjusted level of contrast. <IMAGE>

Description

Control system of video signal processing device

1 is a graph showing a transfer function of a circuit of the invention.

2 is a schematic diagram of a circuit of a first embodiment according to an aspect of the present invention.

3 is a schematic diagram of a circuit of a second embodiment according to an aspect of the present invention.

4 is a schematic diagram of the simplified circuit of FIG.

* Explanation of symbols for main parts of the drawings

5 antenna 12 CRT

20: contrast control device 22, 32: potentiometer

30: luminance control device 38: diode

42: PNP transistor

[Background of invention]

The present invention relates to a video signal processing circuit. In particular, the present invention relates to a luminance signal processing circuit of a color television receiver.

In color television receivers, it is common to provide separate amplification channels for the luminance and chroma signal components of a composite color television signal. The luminance amplifier includes contrast control and luminance control circuits, at least in part operated by the viewer. The contrast control device adjusts the gain of the video amplifier to determine the peak-to-peak amplitude of the trace portion of the video or composition signal supplied to the kinescope or CRT. The luminance control device typically adjusts the black level of the video signal to determine the point at which the electron beam cutoff of the CRT occurs. Typically, the adjusted black level is related to the back porch level of the video signal and the brightness is controlled by the DC insert or clamp circuit. The brightness level may correspond to optical black. But. This "black" level can be adjusted by the viewer to become a higher luminance level, such as gray.

For this purpose, the level setting means for adjusting the brightness of the television receiver is changed by the setting of the amplitude control means for adjusting the contrast, wherein the maximum brightness level for the image on the CRT is directly changed in relation to the adjusted contrast level. .

In this situation, the contrast control by viewer adjustment is Often, brightness control by the corresponding viewer setting is not necessary to maintain a clear black color of the black portion of the image. The advantage of this is that under bright ambient conditions, the luminance adjustment range required to make any acceptable change in the luminance of the details in the dark portions of the scene. It can be understood by considering that it is larger than the required range in low ambient light conditions. Typically. Contrast control will be set at a high level for viewing in high ambient light conditions and at a lower level for darker ambient conditions. like this. Contrast control can be observed as an indication of the viewer's perceived sensitivity to the CRT light output level.

It is not only desirable to avoid excessive brightness control ranges in order to improve "sleep engineering" by providing the viewer with an optimal brightness adjustment range as described above. It is desirable to facilitate certain design constraints within an automatic beam limiter (ABL) device. If excessive luminance control range is allowed. The beam limiter is required to be operated in a more complex manner to effectively limit the beam current. The beam limiter senses the current or voltage associated with the beam current and controls some properties of the video signal to limit the beam current to a predetermined amount. Two of the main video characteristics typically controlled are contrast and luminance. Controlling the brightness to control the beam current is less desirable in the following points than to control the contrast. In other words. The DC component of the video signal changes, and the resolution requires a low beam current because the black level is "black" at that point. Therefore, it is more desirable to reduce the contrast. However, controlling both contrast and brightness allows the viewer to set the contrast as low as possible and widen the range of brightness control so that the CRT is driven with significantly more beam currents, even at very low contrast, so that the brightness is set very high. You need to be prepared. Therefore, typically after detecting excessive beam current, the ABL device first operates to reduce the contrast, and if the reduction in contrast does not keep the beam current of the CRT within a predetermined limit, the second stage of operation reduces the brightness. will be. As such, the design of the ABL device needs to cover the situation of a very high luminance control setting at a low contrast setting that requires the ABL to perform a wide range of luminance control.

For the viewer's extensive brightness control setting, the ABL design chooses a wide range of control for brightness adjustment or a wide range of control for contrast adjustment.

If more than 4 or 5: 1 or more changes in the contrast control capability coupled to the abnormally high viewer's brightness control setting capability are given to the ABL, the result can be severely damaged. As such, a good approach that can be taken to prevent the viewer from having excessive brightness control range is to make the beam limiter more dependent on contrast control.

As such, in order to relieve the burden of compensating for the excessive state described above, it is desirable to design the luminance control range of the viewer as small as possible. In this way, the present invention works to reduce the complexity and possible errors caused by ABL action.

[Overview of invention]

The luminance control is designed to provide a maximum range with the maximum possible luminance setting at the maximum contrast setting. It is recognized here that when the maximum contrast setting is reduced to a lower contrast setting, the maximum range of luminance control may be more than desired. Therefore, it is recognized that it is desirable to use the contrast control information to change the range of the luminance control.

It will be described later with reference to the accompanying drawings for a better understanding of the present invention. In the drawings, the same reference numerals are used for the same elements.

Referring to FIG. 1, there is shown a transfer function in accordance with the present invention in which the luminance control range is changed in accordance with the contrast control setting. The abscissa shows the luminance control setting from 0 to 100 percent, and the ordinate represents the standardized luminance control voltage Vbrt. The transfer function of FIG. 1 has a linear constant slope portion 10, where the output or control voltage Vbrt is independent of the setting of the contrast control and increases linearly with the brightness control setting for the low brightness setting. However, for a high luminance setting above the point 12, the transfer function is a portion 11 that is linearly continuous to the portion 10 when the maximum contrast is set, or a portion having a reduced slope when the minimum contrast is set. It may be any curve in the curve group including (13). The portion 13 and other curves of the curve group should have a slope greater than zero. In another embodiment, the group of curves may have a slope at or near that providing a sharper brightness control cutoff. However, it is recognized that the reduced slope gives the viewer better control of sensitivity.

2 is a schematic diagram of one embodiment implementing the transfer function of FIG. Generally speaking, the television signal received by another suitable signal source, such as antenna 5 or cable system, is processed by tuner 6, intermediate frequency (1F) amplifier 7, and detector 8 to detect the detector. In (8), the luminance signal 9 and the chroma signal 10 are separated. The luminance and chroma signals are appropriately separated and combined in the matrix 11 to drive the CRT 12. Luminance signal processing typically includes amplification and signal processing to implement various luminance signal attributes such as contrast and luminance.

The contrast control device 20 includes a potentiometer 22, which has a variable position wiper arm 24 for changing the voltage output Vpix indicating the contrast or image control setting, and is coupled between ground and the voltage source Vc. The image control voltage Vpix is coupled to the contrast control amplifier 25 in the luminance Y processing channel. In a corresponding manner, the brightness control device 30 includes a potentiometer 32 having a variable position wiper arm 34 for changing the voltage output Vbrt indicative of the brightness control setting and coupled between ground and the voltage source Vb. The luminance control voltage Vbrt is coupled to the luminance control amplifier 35 in the luminance processing channel. Contrast control amplifier 25 and brightness control amplifier 35 are standard implementations commonly used in television receivers to individually control contrast and brightness. The beam limiter control circuit 36 senses the beam current of the CRT 12 and reduces the contrast and / or brightness to reduce the beam current in a manner common to the art in response to the beam current exceeding a threshold. The control amplifier 25 and the brightness control amplifier 35 are affected. As mentioned above, in this manner, the present invention reduces the requirement for a beam limiter.

The non-linear device shown by the diode 38 is coupled between the arm 24 of the contrast control device 20 and the arm 34 of the brightness control device 30 so that the contrast control device 20 from the brightness control device 30 can be obtained. It is positioned to conduct on. Until the nonlinear device 38 starts to conduct, the brightness control and the contrast control operate independently of each other. The isolation resistor 36 is coupled between the anode of the diode 38 and the brightness control device 30. The voltage dividing resistor 40 coupled in series with the diode 38 will be described later in more detail. In the case of the present embodiment, it is assumed that the resistor 40 is bypassed.

Diode 38 will conduct when the net bias voltage from anode (coupled to Vrt) to cathode (coupled to Vpix) exceeds a threshold for the device (which is about 0.55 volts for silicon). Thus, when the wiper arm 34 is positioned to increase the brightness control voltage Vbrt at some threshold voltage (eg, 0.55 volts + Vpix) related to the contrast control voltage Vpix, the diode 38 conducts and clamps Vbrt to the threshold voltage. And will not raise Vbrt anymore. This limits the maximum value of Vbrt that can rise, thereby reducing the maximum brightness at which the image can be adjusted. Since Vpix is an adjustable voltage, the higher Vpix is set (ie, the higher the contrast). Vbrt can be set higher and the maximum luminance of the image becomes higher. Conversely, the lower the Vpix is set, the lower the maximum value of Vbrt and the lower the maximum luminance of the image.

In this case, without the resistor 40, Vbrt is clamped correctly when the diode 38 conducts and the group of luminance transfer function curves is zero slope above a variable threshold voltage (dependent on the position of the contrast controller 20). Has Resistor 40 is an optional resistor that makes the increased voltage slope greater than zero and less than the slope of transfer function portion 11. In this case, once diode 38 is conducting, a voltage drop across resistor 40 occurs and any change in brightness control device 30 setting results in a change in Vbrt. This change in Vbrt is a change in the setting of the luminance control device 30 attenuated by the partial pressure of the resistors 37 and 40 (the anode to cathode voltage across the diode 38 and Vpix are constant). Thus, the resistance ratio between the resistors 37 and 40 determines the increasing slope of Vbrt in the transfer function curve group of FIG.

The control of the luminance level applied to the control of the image level can be implemented in an embodiment including digital analog converters (DACs) 46 and 62 to generate contrast and luminance control voltages, in particular the luminance shown in FIG. Suitable for digital control of processing.

The PNP transistor 42 is a collector electrode coupled to ground. It has a base electrode coupled to a constant control voltage Vpix at the output terminal 47 of the image pix DAC 46 and an emitter electrode coupled to the luminance voltage Vbrt at the output terminal 51. The DAC 46 includes a switching device 46a controlled by a pulse width modulated pulse signal representing a pix control voltage or a pulse of binary speed. The base of transistor 42 is coupled to the junction between resistor 48 (coupled to ground through switch 46a) and resistor 56 (coupled to power supply voltage Vcc). Capacitor 66 is a filter capacitor for DAC 46.

The emitter electrode of transistor 42 is coupled to output terminal 51 of DAC 62 via resistors 52 and 54. The DAC 62 includes a switching device 62a that is similar in function to the switching device 46A. The emitter electrode in transistor 42 is coupled to resistor 58 and switch 62a through resistor 52, which is coupled to ground. Resistor 54 is coupled to the junction between resistor 60 (coupled to Vcc) and resistor 64 (connected to ground). Capacitor 68 is a filter capacitor for DAC 62 and capacitor 67 is a power filter capacitor.

Contrast DAC switch 46a and luminance DAC switch 62a are often included in integrated circuits, such as MC68HC05TV1 manufactured by Motorola. The output circuits of this type of DAC are typically bipolar or MOS transistors, and as switches 46A and 62A in FIG. Is shown.

In FIG. 3, transistor 42 is a non-linear device having a base-emitter circuit having a threshold of conduction corresponding to diode 38 in FIG. Transistor 42 does not conduct until the base electrode is sufficiently forward biased for conduction. Below this threshold of conduction, contrast and brightness control operate independently of each other.

More specifically, the contrast control signal Vpix generated by the DACs 46 and 47 is applied to the base electrode. The luminance control signal Vbrt generated by the DAC 62 and applied to the emitter electrode 51 shunts the transistor 42 in response to the voltage applied from the DAC 46 to the base electrode. Or by a loading action When the conduction threshold of the base-emitter circuit is reached by the voltage generated by the DAC 46, the collector-emitter circuit of the transistor 42 begins to conduct and varies. Shunt is provided to ground The emitter electrode of transistor 42 has a low output impedance, so the Thevenin equivalent output impedance of resistor 52 and luminance DAC switch 62A is essentially the slope of luminance control signal Vbrt above the breakpoint. However, the transistor 42 in FIG. 3 further improves the separation between the contrast circuit and the luminance circuit than the diode 38 in FIG. 2 provides while allowing Vpix to still affect Vbrt. Provided.

3 shows a simplified version of the circuit in FIG. 4 with a resistor 70 representing the taban output impedance of the DAC 62 and a resistor 69 representing the taban output impedance of the DAC 46. The DACs 46 and 62 with their corresponding output switches 46A and 62A are merely embodiments of possible digital implementations of the system described herein. It is seen herein that video signals are converted to digital form and processed digitally in a digital system. While the interaction between contrast control and luminance control is described by an embodiment in terms of an analog circuit comprising a non-linear device, the interaction is accomplished by a microprocessor such as microprocessor 72 in FIG. It may be implemented in digital form, including software control, which are considered within the scope of the above and other amendments.

Claims (4)

Processing means for processing the video signal prior to application to the visual display device comprising a video signal source and a visual display device and luminance processing means for controlling the brightness of the reproduced image and contrast processing means for controlling the contrast of the reproduced image A control system of a video signal processing apparatus comprising: brightness control means coupled to the brightness processing means for adjusting the brightness of the reproduced image to a desired brightness level between a maximum brightness level and a minimum brightness level; Contrast control means, coupled to the contrast processing means, for adjusting the contrast of the reproduced video to a desired contrast level between a maximum contrast level and a minimum contrast level; And changing means for changing the control of the brightness level when there is a predetermined relationship between the brightness level and the contrast level. The control system of a video signal processing apparatus according to claim 1, wherein said changing means comprises a nonlinear element. 2. The control system of claim 1, wherein said changing means comprises digital processing means controlled by software. 9. The control system of claim 8, wherein the software controlled digital processing means comprises a microprocessor.